For many decades small internal combustion engines, such as those used for recreational vehicles and landscaping tools like chain saws, trimmers, tractors, and lawn mowers, have typically used mechanical, manually-operated recoil pull-starters. In a direct recoil pull-starter, an operator of the vehicle or garden tool pulls a cord which is wound about a recoil pulley to rotate the recoil pulley in a first direction. The rotating recoil pulley rotates an engine crankshaft, via a one-way coupling, to start a combustion engine. The one-way coupling allows the crankshaft of the running engine to rotate freely relative to the recoil pulley. When the cord is released by the operator, the recoil pulley automatically reverses rotation, by way of a torsional recoil spring, to retract the cord back around the recoil pulley.
The direct recoil pull-starter is generally satisfactory, but in some applications, may be disadvantageous. In the event that an engine was shut down with the piston before top dead center and with the exhaust and intake valves closed (i.e. during a compression stroke of the engine), pulling of the starter cord may be difficult to say the least. In fact, the cord may actually snap out of an operator's hand back into the pulley housing because the trapped air within the combustion chamber resists compression, essentially keeping the piston and crankshaft in their arbitrarily shutdown positions. The operator must exert a sufficiently large pulling force to overcome such internal resistance during a compression stroke of a piston in the engine.
Making matters more difficult, engine emissions regulations are becoming more stringent, thereby forcing engine manufacturers to increase the compression ratio of their engines to increase power and improve the emissions-to-power ratio. But higher compression ratios yield higher compression forces that must be overcome to start the engine, thereby making such engines relatively more difficult to start by hand. And higher compression ratios also exacerbate the problem of piston bounce between compression strokes during starting, wherein the operator experiences a jerking motion in the pull cord that gets transmitted through the piston, crankshaft, flywheel, coupling, and the pulley to which the cord is attached. Such problems are intensified with engines that have neither a relatively large weighted flywheel nor a slip clutch between an output shaft of the engine and a load.
To alleviate such conditions, many devices use a so-called stored energy recoil spring starter wherein an operator repeatedly pulls a cord, which is wound about a recoil pulley, to rotate the recoil pulley in a wind up direction to progressively wind up a ratchet engaged starter spring. When released by pressing a ratchet release button and release mechanism, the starter spring suddenly unwinds to rotate the recoil pulley in a starting direction opposite the wind up direction. The rotation of the pulley causes a crankshaft to rotate, via a one-way coupling arrangement therebetween, to start the engine. Unfortunately, however, these stored energy starters often require an operator to yank repetitively on the pull cord and are often bulky and heavy in order to accommodate a sufficiently powerful starter spring to overcome the high resistances incurred when starting the engine.
In recent years, however, many manufacturers have incorporated torsional damper springs within recoil pulleys of direct recoil starters. At least one such starter includes a rotatable pulley, a cord wound around the pulley, a recoil spring to rewind the cord, a torsional damper spring coaxial with the pulley and having one end biased against a portion of the pulley and having an opposite end biased against a centrifugal ratchet provided on an engine flywheel. This opposite end of the damper spring is arranged to releasably engage with the centrifugal ratchet so as to transmit forward rotation of the pulley to the flywheel through the ratchet. With this configuration, the shock caused by the engine is absorbed by the damper spring and a rotating force from the pulley is stored by the damper spring. Unfortunately, however, this approach may require redesigning and repackaging one or more of conventional pulleys, flywheels, and coupling mechanisms therebetween. Also, this dampening mechanism is one-dimensional in that it fails to provide additional functionality besides dampening.